Beaded center tube

ABSTRACT

A perforated metal center tube is provided for use within an oil, fuel, or hydraulic filter. The tube is fabricated from a perforated metallic sheet formed into a cylinder in which opposite edges thereof are mutually engaged with one another to form a longitudinal multi-layered lockseam. The lockseam is mechanically clinched to inhibit slippage of the mutually engaged edges without the need for welding, soldering or otherwise chemically or adhesively bonding the lockseam. A series of circumferential beads are provided at spaced locations along the length of the tube to provide structural reinforcement. Each bead is formed through lockseam without generating slippage or disengagement of the first and second edges relative to one another. The beads advantageously provide the tube with sufficient structural integrity to withstand typical filtration pressures, with a metallic sheet of relatively thin gauge.

This application is a continuation of U.S. patent application, Ser. No.09/038,415, filed Mar. 11, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to perforated filter tubes, and more particularlyto a lockseamed center tube having a plurality of circumferential beads.

2. Background Information

A wide variety of perforated tubes for use in fuel, liquid, oil orhydraulic filters have long been known in the art. These tubes aretypically fabricated from perforated metallic sheet or coil stock cut topredetermined size, formed into a cylinder and then seamed alongadjoining edges. These tubes must have adequate structural integrity towithstand relatively high collapse pressures exerted on the tube byfuel, oil, or hydraulic fluid during conventional filtration operations.The thickness or gauge of the sheet or coil stock and the integrity ofseam play important roles in providing the tube with the requisiteresistance to the collapse pressures.

One common approach to tube fabrication is to form a cylinder fromsmooth sheet steel of relatively heavy gauge, and provide a lockseam inwhich the adjoining edges of the sheet are mechanically folded over oneanother. The lockseam thus includes several thicknesses of material andis therefore thicker than the remaining circumference of the tube. Theresulting center tube advantageously includes a structurally rigid tubewall, with the lockseam being sufficiently rigid for filtrationoperations without the need for additional welding or brazing operationsfor savings in labor and capital equipment costs relative to weldedseams.

A drawback of this approach, however, is that the relatively heavy gaugesheet stock represents a large percentage of the material expense of thetube. It is thus desirable to utilize lighter gauge sheet stock, whilestill providing the tube with the requisite structural integrity.

One attempt to overcome this drawback has been to use lighter gaugesheet stock and corrugate it to improve the sheet's structural rigidity.The corrugations are generally applied to the sheet prior to bendinginto tubular configuration. The corrugations are generally terminatedprior to reaching the edges of the sheet, so as not to interfere withfabrication of the lockseam. While corrugations tend to improve therigidity of the tube, they must be kept sufficiently shallow andcurvilinear in profile so as to facilitate tube formation withoutgenerating buckling, etc. This aspect thus tends to substantially limitthe degree of wall rigidity imparted by such corrugations.

An alternative approach is to apply corrugations after tube fabrication.Such post-fabrication corrugating operations have been utilized in themetal can industry and typically include application of pressure to thewall of a can as it rotates about its axis to provide an indentationabout the entire circumference thereof. This approach may enable deepercorrugations for improved strength relative to the aforementionedpre-fabrication corrugations. While this approach may operatesuccessfully for relatively light-duty can making operations, thistechnique, as well as the conventional equipment utilized for thispurpose, has generally been inadequate for use in heavier dutyapplications such as filter tube fabrication involving simultaneousformation of a plurality of corrugations, or fabrication of deeper,generally rectilinear beads. In these instances, the unsoldered,multi-thickness lockseam of the filter tube tends to disengage or popopen.

One approach to ameliorating this popping, may be to weld or solder thelockseam prior to beading, as has been done in the can making industry.However, welding or soldering represents an additional manufacturingstep which tends to add undesirable time and expense to the manufactureof the tube.

This and other techniques utilized in the canning industry are thusgenerally inapplicable to the filtration industry, due to the disparatestructural requirements of these two applications. For example, generalpurpose metal cans such as those used for packaging food or liquids aretypically designed to withstand significantly lower pressures than thoseexperienced by a filter tube of similar size. Moreover, the types ofpressures are also distinct. Many metal cans are designed to withstandinternal or burst pressures, while filter tubes must withstand externalor collapse pressures.

In this regard, corrugations or ribbing applied to general purpose metalcans such as used for food, are typically designed to facilitatehandling, i.e. to provide texture to the surface of the can to helpprevent slippage, and to help the cans resist becoming dented, etc.Contrariwise, deeper corrugations or beads are desired for filter tubesto add substantial rigidity to enable use of lighter gauge sheet stock.

A need thus exists for a filter center tube and method of fabricationthereof, in which a multi-thickness lockseam is capable of being beadedto enable use of relatively light gauge sheet stock.

SUMMARY OF THE INVENTION

According to a first aspect of this invention, a tube adapted for use ina fluid filter includes a perforated metallic sheet formed so that firstand second edges thereof are mutually engaged to form a longitudinallockseam having a plurality of thicknesses of the metallic sheet andbeing free from chemical and adhesive bonds. A plurality ofcircumferential beads are formed at spaced locations along the length ofthe tube to provide structural reinforcement. Each of the plurality ofcircumferential beads is extended through the lockseam withoutdisengaging the lockseam.

The present invention provides, in a second aspect, a method forfabricating a tube for use in a fluid filter. The method includes thesteps of:

(a) providing a metallic sheet having a pattern of perforations disposedthereon;

(b) forming the metallic sheet wherein first and second edges thereofare disposed proximate one another;

(c) mutually engaging the first and second edges to form a longitudinallockseam having a plurality of layers of the metallic sheet and beingfree from chemical and adhesive bonds; and

(d) forming a plurality of circumferential beads at spaced locationsalong the length of the tube to provide structural reinforcement,wherein each of the plurality of circumferential beads is extendedthrough the lockseam substantially without disengaging the lockseam.

The above and other features and advantages of this invention will bemore readily apparent from a reading of the following detaileddescription of various aspects of the invention taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a filter tube of the present invention;

FIG. 2 is a partially cross-sectional plan view of the filter tube ofFIG. 1, during a step in the fabrication thereof;

FIG. 3 is a cross-sectional plan view, on a reduced scale, of anembodiment of a form element utilized to fabricate the filter tube ofFIGS. 1 and 2;

FIG. 4 is a perspective view of an alternate embodiment of a formelement utilized to fabricate the filter tube of FIGS. 1 and 2;

FIGS. 5-8 are end views of various steps in one method of fabrication ofthe filter tube of FIG. 1;

FIGS. 9-12 are end views of various steps in an alternate method offabrication of the filter tube of FIG. 1;

FIGS. 13-16 are end views of various steps in a further method offabrication of the filter tube of FIG. 1;

FIG. 17 is a plan view of an optional step in the fabrication of thefilter tube of FIG. 1;

FIG. 18 is a cross-sectional view taken along 18--18 of FIG. 17;

FIG. 19 is a perspective view of an alternate embodiment of a filtertube of the present invention;

FIG. 20 is a cross-sectional plan view of the filter tube of FIG. 19,taken along 20--20 of FIG. 22, during a step in the fabrication thereof;and

FIGS. 21-23 are schematic end views of various steps in a method offabrication of the filter tube of FIG. 19.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the figures set forth in the accompanying Drawings, theillustrative embodiments of the present invention will be described indetail hereinbelow. For clarity of exposition, like features shown inthe accompanying Drawings shall be indicated with like referencenumerals and similar features as shown in alternate embodiments in theDrawings shall be indicated with similar reference numerals.

Referring to FIG. 1, the subject invention includes a perforated metalcenter tube 20 for use within an oil, fuel, or hydraulic filter. Tube 20is fabricated from a perforated metallic blank or sheet 24 formed into atube or preferably a cylinder, in which opposite edges thereof aremutually engaged with one another to form a longitudinal lockseam 28.Lockseam 28 is formed in a conventional manner in which the edges arefolded over one another to provide the seam with a multi-layeredthickness in the radial direction. In one embodiment of tube 20 asshown, lockseam 28 includes four thicknesses of sheet 24. Lockseam 28 ismechanically clinched or crimped with a herringbone pattern 30 to helpprevent slippage of the mutually engaged edges. Any suitable techniquefamiliar to those skilled in the art may be utilized for this purpose.For example, a conventional crimp die (not shown) may be utilized toapply a predetermined compressive force to the lockseam. In this manner,lockseam 28 provides requisite structural integrity to facilitateformation of beads 32 without the need for welding, soldering orotherwise chemically or adhesively bonding the lockseam, while alsoeliminating any need for reworking the lockseam after beading. A seriesof circumferential beads 32 are provided at spaced locations along thelength of tube 20 to provide structural reinforcement to the tube. Eachbead 32 is formed through lockseam 28 without generating slippage ordisengagement of the first and second edges relative to one another.Beads 32, which will be discussed in greater detail hereinafter,advantageously provide tube 20 with sufficient structural integrity towithstand typical filtration pressures, with a metallic sheet 24 ofrelatively thin gauge or thickness t. The perforation pattern, includingdiameter of each perforation 25 and spacing therebetween, ispredetermined to provide desired fluid flow therethrough while providingthe tube with sufficient structural integrity for a given application.Moreover, in one embodiment as shown, the perforation pattern ispredetermined so that the beads 32 and lockseam 28 are free fromperforations for enhanced strength.

As used herein, the terms "longitudinal" and "axial" shall refer to adirection parallel to central axis 36 of a cylindrical tube of thepresent invention. Similarly, the term "radial" shall refer to adirection extending orthogonally from the central axis, and the term"circumferential" shall refer to a direction along the circumference orperiphery of a cylindrical tube of the present invention.

Referring now to FIG. 2, beads 32 are formed in tube 20 by fitting thelockseamed sheet 24 (FIG. 1) over a cylindrical support or mandrel 38which is provided with a series of annular troughs or grooves 40 sizedand shaped to define the beads. Mandrel 38 is adapted to rotate aboutits central axis 42 which is effectively cammed into mating engagementwith a form element 44 having series of projections 46. Projections 46are sized and shaped for metal forming receipt within troughs 40.Movement of mandrel 38 and element 44 towards one another moves theprojections into engagement with portions of sheet 24 and thenplastically deforms those portions into respective troughs 40 to formbeads 32 as shown. The rotation of mandrel 38 serves to form the beadsalong the complete circumference of cylindrical sheet 24, includingthrough lockseam 28, to form a completed center tube 20 as best shown inFIG. 1.

Troughs 40 and projections 46 have a substantially rectilinear axialcross-section, which, as shown, forms beads 32 having a similarrectilinear cross-section as defined by bottom portions 54 ofsubstantially flat cross-section and which extend axially a distance d1approximately greater or equal to the radial depth d2 of the bead.Bottom portion 54 of each bead 32 thus substantially defines acylindrical surface. This rectilinear profile generally provides tube 20with greater structural integrity than would conventional corrugationswhich generally utilize an undulating or sinusoidal axial cross-section.

As also shown, in one embodiment, form element 44 includes a liner 48disposed between projections 46. Liner 48 may be sized to provide apredetermined clearance c with tube 20 at the nip point or point ofclosest proximity between element 44 and mandrel 38 when disposed intheir fully engaged orientation as shown. Clearance c is predeterminedto permit liner 48 to engage and apply pressure to lockseam 28 as thelockseam passes through the nip point. Clearance c enables liner 48 tobe fabricated from a relatively rigid material, such as a metallicmaterial formed integrally with mandrel 38.

However, the liner is preferably fabricated from a resilient materialsuch as rubber or polyurethane. In this regard, the durometer hardnessof the material is predetermined to apply sufficient pressure tosubstantially prevent the lockseam from buckling or "popping" orotherwise disengaging during the beading operation. The predetermineddurometer hardness also provides sufficient resilience to permit theradial thickness of the lockseam to vary along its length due to thestresses generated by the beading operation. Clearance c is preferablyequal to or less than the nominal thickness of sheet 24 multiplied bythe number of extra sheet thicknesses (i.e. greater than one sheet, asshown) in lockseam 28. This provides a clearance c between the unseamedportion of tube 20 and liner 48 equal to or less than three times thethickness of sheet 24 as shown. The particular size or magnitude ofclearance c, if used at all, is determined in combination with theresiliency or hardness of liner 48. For example, a relatively largerclearance c may be utilized for relatively hard or unresilient linerssuch as those fabricated from metal or hard rubber or plastic. A smallerclearance c may be utilized with liners having a lower durometerhardness in order to apply the requisite pressure to lockseam 28 duringbeading operations. In a preferred embodiment, liner 48 is provided withsufficient resiliency to enable clearance c to be substantiallyeliminated or reduced to zero so that the liner may supportably engageboth the seamed and unseamed portions of the tube during the beadingoperation. Examples of materials suitable for the liner include naturalrubber and synthetic rubbers that exhibit good tear and abrasionresistance, while also being resistant to lubricating oils commonlyassociated with metal fabrication. Examples of synthetic rubbers whichmay be utilized in the present invention include polyurethanes or otherpolymers or copolymers including polybutadiene rubbers (BR),polyisoprene rubbers (IR), fluorinated rubbers such aspolytetrafluoroethylene (PTFE), polyimide, acrylates, butyl rubber(IIR), chlorosulfonated polyethylene, neoprene, nitrile rubbers (NBRs),thermoplastic rubbers, or blends thereof with or without fillers orsubstrates. The liner thus permits lockseam 28 to expand radially apredetermined extent on either side and proximate each bead 32, wherestress concentrations are relatively high. The liner will tend toprevent expansion of the lockseam at positions further from beads 32where stresses generated by the beading operation are relatively low. Inthis manner, liner 48 facilitates the formation of relatively deeprectilinear beads for added tube strength relative to the lessstress-inducing undulating pattern of conventional corrugations.

Turning now to FIG. 3, in one embodiment, form element 44 is fabricatedas a substantially cylindrical roll 144. The projections include aseries of annular rings 146 with a liner 148 disposed therebetween. Roll50 is adapted to rotate about its longitudinal axis 50 during beadingoperations as will be discussed hereinbelow.

A further embodiment of form element 44 is shown as rail 244 in FIG. 4.Rail 244 includes a plurality of elongated projections 246 with liner248 disposed therebetween.

One embodiment of the beading operation of the present inventionutilizes a roll 144 and is shown in FIGS. 5-8. Roll 144 and mandrel 38may be disposed on any suitable apparatus (not shown) such as a manualor automatic machine of the type commonly utilized for applyingcorrugations to metallic cans, in which the roll 144 and mandrel 38travel in a planetary manner relative to one another during operation.

As shown in FIG. 5, the unbeaded tube, including lockseam 28 andherringbone clinch 30, is placed concentrically over mandrel 38 which isdisengaged from roll 144. Roll 144 is then rotated on its axis as shownby arrow 56 as the roll is cammed into contact with sheet 24 as shown inFIG. 6. Such contact tends to rotate mandrel 38 and sheet 24 in thedirection indicated by arrow 58. Roll 144 and/or roll 58 is graduallycammed into full engagement with mandrel 38 as the rotation of the roll,mandrel and tube forms beads 32 about the complete circumference of thetube, including lockseam 28. Mandrel 38 and roll 144 are subsequentlycammed away from one another until fully disengaged as shown in FIG. 8to permit removal of the beaded tube 20 from mandrel 38.

An alternate method of providing beads 32, utilizing mandrel 38 and rail244 is shown in FIGS. 9-11. This method is substantially similar to thatshown in FIGS. 5-8. In particular, the unbeaded tube is placed overmandrel 38 in the step shown in FIG. 9. The mandrel travels along an arctowards a curved rail 244. The radius of curvature of rail 244 isgreater than that of the arc along which the mandrel travels. Thismovement of the mandrel relative to the rail thus serves to effectivelycam mandrel 38 into initial engagement with rail 244 as shown in FIG.10. Continued movement of mandrel 38 tends to roll the mandrel alongcurved rail 244 into tighter engagement with the rail until fullengagement is reached, as shown in FIG. 11. Further arcuate movement ofthe mandrel moves it away from the rail to its disengaged position shownin FIG. 12, for removal of the beaded tube 20.

In a still further variation of the beading operation, mandrel 38 may berotated about a roll 144 that rotates about a stationary axis as shownin FIGS. 13-16. Mandrel moves from a disengaged position (FIG. 13) fortube insertion, to initial engagement (FIG. 14), full engagement (FIG.15), and to its disengaged position (FIG. 16) for removal of the beadedtube 20.

Turning now to FIGS. 17 & 18, it may be desirable to provide tube 20with a series of indentations or "pre-beads" 34 prior to formation ofbeads 32 (FIG. 1). This optional step may be particularly useful whenbeading a tube 20 fabricated from a sheet 24 of relatively largethickness. Conversely, it may be desirable to omit this pre-beading stepwhen beading tubes fabricated from lighter gauge sheet 24. In thisoptional step, pre-beads 34 are disposed along seam 28 at spacedlocations predetermined to align with projections 46 (FIG. 2) duringsubsequent beading formation. As shown in FIG. 18, the pre-beads arepreferably provided with a cross-sectional profile of substantiallysimilar size and shape to that of beads 32 (FIG. 2). In this manner,seam 28 is effectively beaded before the remainder of the tube. Whensubsequently formed as described hereinabove, beads 32 (FIG. 1) willextend continuously about the circumference of the tube, throughpre-beads 34. This pre-beading step substantially eliminates the need tobend the multi-thickness seam 28 during the aforementioned formation ofbeads 32 as discussed hereinabove with respect to FIGS. 2-16. This stepthus advantageously smooths the transition between the single thicknesssheet 24 and the multiple thickness seam 28 for smoother beadingoperation. Pre-beading seam 28 in this manner also tends to enableformation of beads 32 using relatively less engagement force betweenprojections 46 (FIG. 2) and the tube. Pre-beading thus advantageouslytends to reduce stress and wear on the beading apparatus, while it alsoenables formation of relatively deeper beads 32. Pre-beads 34 may beformed by any convenient method known to those in the metal workingfield, such as by striking tube 20 with a suitable tool sized and shapedto provide the pre-beads with the desired geometry.

The present invention thus enables center tubes 20 to be fabricated withrelatively light gauge metallic sheet while being able to withstandpressures commonly associated with fluid filtration, such asapproximately 50-100 psi.

Sheets of substantially any thickness may be utilized. However,thicknesses within a range of approximately 0.007-0.010 in (0.1-0.2 mm)are preferred for tubes of approximately 1.0-2.0 in (25-50 mm) indiameter.

Tube 20 may be fabricated from a wide range of materials, such as, forexample, tin plate, cold rolled steel, flashcoated zinc, stainlesssteel, aluminum, brass and ferrous or non-ferrous alloys. The tube maybe provided with any number of sizes, ranging from less than 2 cm indiameter to 25 cm or more. Lengths of the tubes may be anywhere fromapproximately 2 cm to 130 cm or more.

Tubes 20 constructed in accordance with the present invention have beenshown to withstand collapse pressures common to liquid or hydraulicfiltration operations without the need for additional operations such aswelding, brazing, soldering or post-beading re-work of the lockseam.This result is surprising in light of prior art beaded cans and the likewhich tended to utilize both solder or braze on the lockseams andshallow undulating corrugations rather than the rectilinear beads of thepresent invention.

Although tube 20 has been described as being applied to a liquid filter,the tube and fabrication methods of the present invention may be used invarious other applications such as air or gas filtration andconventional metal can fabrication.

Although tubes of the present invention have been shown and describedherein having circular transverse cross-sections, it should be apparentto those skilled in the art that substantially any cross-sectionalgeometry may be utilized without departing from the spirit and scope ofthe present invention.

A further embodiment of the present invention is shown in FIGS. 19-23.Turning to FIG. 19, a perforated metal center tube 20' is substantiallysimilar to tube 20, though a `squeezing` method is utilized to fabricatebeads 32', as will be described hereinbelow. The resulting beads 32',are provided with pinched portions 70 placed at predetermined, spacedlocations along the beads 32' which correspond to the junctions 74 (FIG.22) of die portions 46' as will also be discussed hereinbelow. Lockseam28 of tube 20' may be provided with a clinch or crimp, such as theherringbone crimp pattern 30 as shown, or may be optionally fabricatedwithout the crimp.

Referring to FIG. 20, the beads 32' are formed in tube 20' by fittingthe unbeaded tube or tubular sheet 24 concentrically with a series ofinner dies 72. Each of the dies 72 are provided with annular troughs orgrooves 40 adapted to engage the inner surface of the tube as shown. Theinner dies 72 are adapted to move radially outwardly and inwardly toalternately engage and release the tube. A series of form elements 44'are also radially movable to alternately engage and release an exteriorsurface of the tube, as will be discussed in greater detail hereinbelow.The form elements 44' are provided with a series of projections 46 whichare sized and shaped for metal forming receipt within troughs 40.Movement of the inner dies 72 and elements 44' towards one another movesthe projections into engagement with portions of sheet 24 and thenplastically deforms those portions into respective troughs 40 to formbeads 321 as shown.

Each element 44' may be fabricated as a one piece device (as shown), oralternatively, may be provided with a liner 48 fabricated from apolymeric or metallic material as shown and described hereinabove withrespect to FIG. 2. Whether or not a discrete liner 48 is utilized,clearance c is provided between the tube and the portion of the elements44' disposed between the projections 46. The clearance c may bepredetermined to permit liner 48 to engage and apply pressure tolockseam 28 as the lockseam passes through the nip point, as discussedhereinabove. Alternatively, forming the beads 32' by this squeezingtechnique enables the clearance c to be sufficiently large toeffectively preclude such engagement of the elements 44' with thelockseam 28. Such lack of contact between projections 46 may bepermitted because unlike the sequential bead fabrication techniquesdescribed hereinabove with respect to FIG. 2, the inner dies 72 providesimultaneous support to opposite sides of the inner surface of tube 20'during bead formation. This support tends to restrict radial or lateraldisplacement of the tube during bead formation, to substantially reduceany tendency for the seam to pop or otherwise loosen during beadformation in the lockseam 28. In this manner, rather than proceedingsequentially, the beading of nominally each point or portion along thecircumference of the tube is performed simultaneously. Advantageously,this aspect tends to simplify the beading process relative to otherapproaches.

Turning now to FIGS. 21-23, in an initial step of this beading process,the inner dies 72 are retracted to a radially innermost position toprovide sufficient clearance for unbeaded cylindrical sheet 24 to beplaced concentrically thereover. As also shown, the outer form elements44' are disposed in radially outermost positions which providesufficient clearance for the concentric placement of the tubular sheet24. Turning to FIG. 22, in a subsequent step, dies 72 are moved radiallyoutward into engagement with the inner surface of sheet 24, whileelements 44' are moved radially inward whereby the projections 46effectively squeeze into full engagement with grooves 40 to form thebeads 32' (FIGS. 19 and 20).

The pinched portions 70 (FIG. 19) of the beads are formed at thejunction 74 of adjacent elements 44', as mentioned hereinabove. In apreferred embodiment, the junctions 74 are circumferentially offset fromgaps 76 disposed between inner dies 72 when in their radially outermostposition as shown. This offset helps to maintain support on at least oneside of the tubular sheet 24 during beading. Also as shown, lockseam 28is preferably circumferentially offset from both the junctions 74 andgaps 76 during beading, so that a die 72 and an element 44' both engagethe lockseam to help ensure adequate support therefor during beading.

As shown, four elements 44' are provided, each of which are providedwith a projection 46 sized and shaped to form an approximately 90 degreeportion of bead 32'. Similarly, three inner dies 72 are provided, eachhaving a groove 40 sized and shaped to form an approximately 120 degreeportion of bead 32'. However, any desired number of inner dies 72 andouter elements 44', being sized and shaped to form any suitable arcuateportions of bead 32', may be utilized.

Turning to FIG. 23, in a further step, dies 72 are moved radially inwardand elements 44' are moved radially outward, to clear and release thefully beaded tube 20' to permit the tube to be withdrawn from the dies72.

The foregoing description is intended primarily for purposes ofillustration. Although the invention has been shown and described withrespect to an exemplary embodiment thereof, it should be understood bythose skilled in the art that the foregoing and various other changes,omissions, and additions in the form and detail thereof may be madetherein without departing from the spirit and scope of the invention.

Having thus described the invention, what is claimed is:
 1. A tubeadapted for use in a fluid filter, said tube comprising:a perforatedmetallic sheet formed so that first and second edges thereof aremutually engaged to form a longitudinal lockseam having a plurality ofthicknesses of said metallic sheet and being free from chemical andadhesive bonds; a plurality of circumferential beads formed at spacedlocations along the length of said tube to provide structuralreinforcement; wherein each of said plurality of circumferential beadsis extended through said lockseam while substantially maintaining saidmutual engagement.
 2. The tube of claim 1, wherein said plurality ofcircumferential beads are formed by the process of:(a) engaging anexterior surface of the tube simultaneously at a plurality ofcircumferential locations along at least one of said spaced locationswith a plurality of forming element portions each having a projectiondisposed thereon, the projections being sized and shaped to form aportion of a bead; (b) applying pressure to an interior surface of thetube simultaneously at a plurality of circumferential locations thereon,wherein the plurality of forming element portions plastically deformsthe tube to form the portion of the bead.
 3. The tube of claim 2,wherein said engaging step (a) further comprises the step of engagingthe exterior surface of the tube simultaneously at a plurality oflocations spaced about the entire circumference of the tube with theplurality of forming element portions.
 4. The tube of claim 3, whereinsaid applying step (b) further comprises applying pressure to theinterior surface of the tube simultaneously at locations spaced alongsubstantially the entire circumference thereof, wherein eachcircumferential portion of the bead is formed simultaneously.
 5. Thetube of claim 2, wherein said applying step (b) further comprisesapplying pressure to the interior surface of the tube simultaneously atlocations spaced along the circumference thereof.
 6. The tube of claim5, wherein the tube is adapted for being disposed concentrically with aseries of inner die portions each having an annular trough adapted toengage the inner surface of the tube, the inner die portions beingadapted to alternately move radially outwardly and inwardly torespectively engage and release the tube.
 7. The tube of claim 1,further comprising the step of providing an indentation in saidlongitudinal lockseam at least one of said spaced locations prior toformation of said plurality of circumferential beads.
 8. The tube ofclaim 1, wherein said longitudinal lockseam is mechanically clinched toinhibit release of said mutually engaged edges during beading, saidmechanical clinching comprising the step of providing said longitudinallockseam with a pattern of indentations along the length thereof.
 9. Thetube as set forth in claim 1, wherein said tube is substantiallycylindrical and each of said plurality of circumferential beadscomprises a substantially cylindrical surface disposed concentricallywith said tube.
 10. The tube as set forth in claim 9, wherein each ofsaid plurality of circumferential beads is substantially rectilinear inan axial cross-section.
 11. The tube as set forth in claim 1, whereinsaid longitudinal lockseam comprises at least four thicknesses of saidsheet.
 12. The tube as set forth in claim 1, wherein said beads are freefrom perforations.
 13. A method for fabricating a tube for use in afluid filter, said method comprising the steps of:(a) providing ametallic sheet having a pattern of perforations disposed thereon; (b)forming the metallic sheet wherein first and second edges thereof aredisposed proximate one another; (c) mutually engaging the first andsecond edges to form a longitudinal lockseam having a plurality oflayers of said metallic sheet and being free from chemical and adhesivebonds; (d) forming a plurality of circumferential beads at spacedlocations along the length of said tube, wherein each of the pluralityof circumferential beads is extended through said lockseam whilesubstantially maintaining said mutual engagement of said first andsecond edges.
 14. The method of claim 13, further comprising the step of(e) clinching said longitudinal lockseam prior to said forming step (d),to inhibit movement of said mutually engaged edges relative to oneanother.
 15. The method as set forth in claim 13, wherein said formingstep (d) further comprises the steps of:(f) engaging the tube with aforming element having at least one projection disposed thereon, said atleast one projection being sized and shaped to form a portion of a bead;(g) applying pressure between the tube and the forming element, whereinthe forming element plastically deforms the tube to form the bead; (h)simultaneously engaging the forming element with locations spaced aboutthe entire circumference of the tube to form at least one of theplurality of circumferential beads.
 16. The method of claim 15, whereinthe forming element comprises a plurality of discrete element portionsdisposed in spaced relation about the circumference of the tube, eachsaid element portion being movable radially inwardly and outwardly toselectively engage and release the tube.
 17. The method as set forth inclaim 16, wherein the forming element further comprises a liner adaptedto engage the lockseam proximate the projection during beading of thelockseam.
 18. The method as set forth in claim 16, wherein said engagingstep (h) further comprises the steps of:engaging an interior surface ofthe tube with a die, the die having at least one receptacle adapted toreceive the at least one projection therein.
 19. The method as set forthin claim 18, wherein the die further comprises a plurality of dieportions adapted for engagement with the tube at locationscircumferentially spaced along an interior surface thereof.
 20. Themethod of claim 19, wherein the plurality of die portions are disposedat spaced locations along the entire internal circumference thereof. 21.The method of claim 19, wherein said plurality of die portions aremovable radially inwardly and outwardly to alternately release andengage the tube.
 22. The method as set forth in claim 13, wherein themetallic sheet is free from perforations at predetermined areas so thatthe beads are free from perforations.
 23. The method as set forth inclaim 14, wherein said clinching step (e) further comprises providingthe longitudinal lockseam with a pattern of indentations along thelength thereof.
 24. The method as set forth in claim 13, wherein saidforming step (d) further comprises providing at least one of theplurality of circumferential beads with a surface having a substantiallystraight axial cross-section.
 25. The method as set forth in claim 24,wherein the surface is substantially cylindrical.
 26. The method as setforth in claim 13, wherein said forming step (d) further comprisesproviding at least one of the plurality of circumferential beads with asubstantially rectilinear axial cross-section.
 27. The method as setforth in claim 13, wherein said longitudinal lockseam comprises at leastfour thicknesses of said sheet material.
 28. The method as set forth inclaim 15, wherein said forming step (d) further comprises the stepof:(i) providing an indentation in said longitudinal lockseam at leastone of said spaced locations prior to said engaging step (f).
 29. Amethod for fabricating a filter tube adapted for use in a fluid filter,said method comprising the steps of:(a) providing a metallic sheethaving a pattern of perforations disposed thereon; (b) bending themetallic sheet wherein first and second edges thereof are disposedproximate one another to form a tube; (c) mutually engaging the firstand second edges to form a longitudinal lockseam having a plurality oflayers of said metallic sheet and being free from chemical and adhesivebonds; (d) forming a plurality of circumferential beads at spacedlocations by engaging the sheet between an internal die and a formingelement, the forming element having at least one projection sized andshaped for metal forming receipt by the internal die to form the bead,the forming element having a plurality of element portions disposed atspaced locations along the circumference of the tube and adapted forradial movement to selectively engage and release the tube, the internaldie having a plurality of die portions disposed at spaced locationsalong the internal circumference of the tube and adapted for radialmovement to selectively engage and release the tube; (e) moving theelement portions and the die portions into mutual engagement with thetube to apply pressure to the tube, wherein the tube is plasticallydeformed to form the bead, the bead extending through said lockseamabout substantially the entire circumference of the tube.